A two-phase well purging method has recently been developed for groundwater sampling, with a high-flow rate pumping phase followed by low-flow rate purging and sampling. The high pumping rate causes rapid well decline and increases aquifer hydraulic gradients. The stressed flow field is maintained after switching to a low pumping rate to prevent the water in the well casing from migrating downwards and biassing the collected samples. The determination of the pumping switch time and the transition time interval available for groundwater sampling are two practical challenges that are crucial for using such a sampling approach.
